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History and thorough exam lead to diagnosis
Heart problems that cause sudden death in children often are uncovered following a tragedy. At that time, health care professionals look at other members of the family to see if there is a heredity disorder that resulted in the death.
That’s why public awareness of Sudden Arrhythmia Death Syndrome (SADS) is important, says Peggy Strieper, MD, director of pacing and electrophysiology at the Sibley Heart Center at Children’s Healthcare of Atlanta. People need to know the warning signs so they will recognize a problem in a child before a death occurs and an evaluation of the family is conducted in retrospect, says Strieper.
SADS encompasses a number of different cardiac arrhythmia problems that can cause sudden death in the young. These conditions include long QT syndrome, hypertrophic cardiomyopathy, and arrhytmogenic right ventricular dysplasia.
One of the most common electrical abnormalities of the heart is long QT syndrome, which is an abnormal electrical resetting of the heart. With long QT syndrome, the electricity takes longer to reset itself when it travels from the top chamber to the bottom chamber of the heart. The measurement on the electrocardiogram (EKG) of the electricity moving down through the lower chambers and then resetting itself is called the QT interval. The QT interval represents the duration of ventricular depolarization and subsequent repolarization, beginning at the initiation of the Q-wave of the QRS complex and ending where the T-wave returns to isoelectric baseline. QT interval prolongation creates an electrophysiological environment that favors the development of cardiac arrhythmias. When patients have long QT syndrome, it takes longer for the resetting to occur, so there is a longer measurement on the EKG.
"If it takes longer and your heart all of a sudden starts beating faster, you almost have a collision of the electrical forces with the electricity coming down from the top chamber and it hasn’t reset itself yet," says Strieper.
People who have long QT syndrome frequently have fainting episodes. However, these are not your usual episodes where a person gets light-headed and dizzy, begins to see spots before his or her eyes, followed by tunnel vision, and then passes out. People who have long QT syndrome faint without any sort of warning sign, says Strieper.
This fainting episode might happen during exercise, an emotional outburst, when an alarm clock sounds, when there is a loud noise, or when a person is out in the water swimming. "Those are all red flags that need to be evaluated," says Strieper.
In addition to fainting, some patients complain that their heart is beating faster or irregularly. An irregular heartbeat during or immediately after exercise and fainting while playing sports or immediately after may be signs of long QT syndrome.
Making the diagnosis
One way a diagnosis is made is to have the patient run on a treadmill to see if it will induce a ventricular tachycardia or abnormal lengthening of the QT interval on an EKG. Normally, when people exercise, their heart rate goes up; it takes less time for the heart to reset itself, so the QT interval shortens and shortens, says Strieper. People with long QT syndrome have inappropriate lengthening of the QT interval with exercise and if the timing is just right, they can end up inducing ventricular tachycardia.
For children, it is a good idea to have a pediatric cardiologist do the tests, says Strieper. Although adults have fairly standard EKGs, they can vary with children. As a result, someone who is used to evaluating pediatric EKGs needs to interpret it. "The diseases that we deal with are so different than what an adult cardiologist deals with it would be like having a 70-year-old [patient] come and see me to discuss coronary artery disease," said Strieper.
If long QT syndrome is found, the pediatric cardiologist will test other family members because the condition tends to run in families. If the mother or father has long QT syndrome, there is a 50% chance that their child will inherit it. Often when a child is referred, although he or she may have been diagnosed correctly, no family members have been screened, such as the siblings and cousins. "If you forget to look at everyone, you could still have a tragedy," says Strieper.
In addition to an EKG to see if the QT interval is long, pediatric cardiologists also get a detailed family history. Usually when asked if there is a family history of sudden death, families will say no. However, when questioned more carefully, they will say that an uncle drowned even though he was a good swimmer or drove off the road and was killed in a car crash. These could be signs that long QT syndrome runs in the family.
Anyone who works with children, including teachers and coaches, needs to be aware of long QT syndrome. If a child passes out after exercise or complains of an irregular heartbeat, he or she needs to see a physician. Most importantly, when parents suspect that their child has been misdiagnosed, they must ask to see a specialist. "It is always difficult, but parents need to be their child’s advocate," says Strieper.
For more information about long QT syndrome, contact:
• Peggy Strieper, MD, Director of Pacing and Electrophysiology, Sibley Heart Center, Children’s Healthcare of Atlanta. Telephone: (404) 256-2593.
• The Sudden Arrhythmia Death Syndromes Foundation, 508 E. South Temple, Suite 20, Salt Lake City, UT 84102. Telephone: (800) 786-7723 or (801) 531-0937. Web site: www.sads.org.